1. Field of the Invention
The present invention relates to an optical wave guide and a method for producing the same.
2. Description of the Background Art
In a conventional optical wave guide, quartz material is employed, and a core and a cladding layer are formed by applying ion implantation, ion exchange, or the like to the quartz material. Therefore, its production process required a semiconductor production process employing highly priced facilities and devices, leading to high costs.
Some trials have been conducted wherein low costs of optical wave guides are attained by producing optical wave guides by reproduction method (or stamper method). The most simple and low cost method in reproduction methods may be that core material (transparent resin) is only applied onto the surface of a cladding substrate on which a groove to be an optical wave guide core is formed by a stamper. Alternatively, an applied core material is pressed flat. However, the former method only applying a core material brings about concaves and convexes on a surface of the core, and light may reflect diffusely on the surface of core and light in the core may leak out. Further, the latter method of pressing an applied core material, light in the core may leak out through a portion of the core material pressed and extended on the surface of a cladding layer. As a result, in these methods, deterioration of characteristics such as decline of S/N ratio of a light signal and the like may occur. Therefore, it has been impossible to produce optical wave guides that meet required standards.
Accordingly, the following improved reproduction methods have been proposed conventionally. For instance, according to the method for producing a high polymer optical wave guide disclosed in Patent Publication (Unexamined) No.63-281351, a groove to be an optical wave guide core is formed on the surface of a cladding substrate by means of reproduction using a stamper, and a core material (transparent resin) is poured into the groove. After this core material hardens, excessive core material protruding from the groove is cut out, thereby an optical wave guide core is formed within the groove.
According to a method for producing a high polymer optical wave guide disclosed in Patent Publication (Unexamined) No.9-281351, core material is applied into grooves reproduced on a cladding substrate. Then, before the core material hardens, unnecessary core material protruding from the groove is scraped off by a rubber pallet, a scraper, or the like, and thereafter the core material is hardened.
These reproduction methods as mentioned above enable optical wave guides to be produced with simple production facilities and through simple production process. Therefore, they are advantageous in producing extremely low priced optical wave guides. However, these methods for producing optical wave guides by the reproduction method have had the following problems.
First, in the former method wherein core material is cut off after core material hardens, because the refractive indexes of cladding substrate and core are not so large, the border surface of the core and the cladding layer is hard to see, and consequently it is difficult to judge to what extent the core should be cut off. Further, when the core is removed by grinding, since the thickness of applied core material and the thickness of cladding substrate are uneven, an unnecessary portion of core material may be removed completely, or the cladding substrate may be cut off excessively. If an unnecessary portion of core material is left, leakage of light cannot be prevented and yield decreases. Also, if the cladding substrate is cut to excess, its core size changes, resulting in optical wave guides having different characteristics. In contrast to this, if core is to be cut carefully and individually, the hassle of labor increases, and productivity decreases. As a result, product costs become high.
In the latter method wherein core material is scraped off before the core material hardens, it is difficult to completely remove the core material in unhardened status by a rubber pallet or the like, and an unnecessary portion of the core material may be left on cladding substrate. Further, when the unnecessary core material is left partially, it is not possible to confine light within the core, resulting in yield loss. Furthermore, if the excessive core material is scraped completely off by the rubber pallet or the like, the surface of the core material becomes concave based on surface tension of the core material. If the core material is harden in such status, the concave shape of the core surface remains as it is. As a result, performance of confining light is deteriorated, and S/N ratio decreases. In addition, different characteristics appear, resulting in yield loss.
Additionally, in U.S. Pat. No. 2,679,760, an optical wave guide where slots are arranged at both sides of core is described. However, in this optical wave guide, the top surface of the core is not released. Further, unnecessary core material does not flow from the core into slots. In Patent Publication (Unexamined) No.9-101425, space is formed at both sides of a groove arranged on cladding substrate. However, this is for core material remaining in the groove even after spin coating, and core material in groove exists only at the bottom of groove. Also, the core material within the groove does not flow into a space when pressed by an upper cladding portion.